James Harden's "perfect mindset" was lauded by Doc Rivers after the Philadelphia 76ers got the better of the Boston Celtics.

The 76ers nudged themselves ahead in their Eastern Conference semifinals series against the Celtics with a 119-115 win on Monday.

Philadelphia were without talisman and NBA MVP candidate Joel Embiid, who was ruled out of Game 1 due to a sprained ankle.

Yet Harden stepped up, scoring 45 points, matching his playoff career-high.

"I thought that he had just the perfect mindset tonight," 76ers coach Rivers said of Harden.

"He really did. I'm so happy for him because it just tells you what he can do on given nights.

"The guy is a Hall of Famer, and all you hear is the other stuff about him, and he was fantastic."

Harden finished with 17-for-30 from the field and 7-for-14 three-pointers.

"I haven't felt one of those zones in a minute," Harden said. "You know what I mean? Just to be aggressive and shoot the basketball and do what I want.

"That felt really good. I'm capable of doing it, so it felt good. It felt good to make those shots, to give ourselves a chance."

Harden, though, does not feel he needs to prove himself all over again – he just wants to help the Sixers win.

"I don't need to make a statement," Harden added. "My coaches, my team-mates, what they expect me to do all throughout the course of the year was be a facilitator and get Joel the basketball and score when necessary. Joel wasn't here tonight, you know what I mean? And, we knew that going into this series.

"Now it's like, 'All right, open the floor. James, you be aggressive.' And tonight, I was aggressive. So, it's not that I'm not capable of doing it, this is my role for this team. Now, if you want me to do [what I did] tonight, then I can do that as well.

"I don't think a lot of players can do that. So yeah, I appreciate that."

For Harden's team-mate P.J. Tucker, Monday's win was evidence the Sixers are not wholly reliant on star player Embiid.

"I think we take pride in playing without the big fella," Tucker said. "As good as he is, I think it gives others opportunities to step up and play.

"Everybody took a little step up with him out. It's like a pride thing for us."